In such boat drives a propeller is fixed to the drive output end of the propeller shaft, which during operation provides the propulsion of the boat when the propeller shaft is rotating. With the help of the swiveling underwater housing the travel direction of the boat can be changed, since when the underwater housing is swiveled the propulsion vector produced by the rotating propeller also changes its direction.
WO 02/24522 A1 describes such a boat drive with an underwater housing arranged outside of and able to swivel relative to the boat hull. In this boat drive, a propeller shaft that can be driven in rotation is arranged in the underwater housing. The swiveling movement of the underwater housing is brought about by a swivel drive mechanism with a swivel drive motor arranged on the inside of the boat hull.
A further boat drive with an underwater housing arranged and able to swivel underneath the boat hull is known from WO 2005/005249 A1. in this case the propeller shaft mounted in the underwater housing and its associated propeller are driven by a drive motor arranged inside the boat hull by way of two bevel gear transmissions and the corresponding driveshafts. Here too, the swiveling movement of the underwater housing is brought about by a swivel drive mechanism with a swivel drive motor arranged on the inside of the boat hull.
In WO 2010/094612 A1 as well, a boat drive of similar type with a swivel drive mechanism in the form of a control device is described, In that case a boat drive with a swivel drive mechanism is described, in which to control the travel direction an underwater housing with a propeller can be swiveled with the help of two electric servomotors as swivel drive motors.
Furthermore WO 10037744 A2 describes a device for detecting an angular position of a swivel control shaft in connection with a boat drive of the type described at the start, such that with the device the current swivel position of the swiveling underwater housing is detected and used for controlling a motorized swivel drive mechanism.
All the documents mentioned lack any indication about whether or how the boat drives described can be controlled in the event that the swivel drive motors or their controls should fail. Methods are known, in which after a failure of the swivel drive motor the swivel drive mechanism of such a boat drive can be actuated manually from inside the boat hull. In this, however, it is disadvantageous that the current swivel position of the underwater housing cannot be recognizer from inside the boat.